Hemorrhagic shock is a major cause of death in emergency departments and trauma centers. Currently there is no clinically accepted quantitative monitor of the onset of hemorrhagic shock. Death from hemorrhagic shock results from diminished capillary blood flow and the resultant failure of the body to oxygenate major organs. The long-term goal of this proposal, a collaboration between Radiation Monitoring Devices and the Mayo Clinic, is to develop a sensor patch (CBFM) that attaches to a patient's skin and continuously monitors capillary blood flow and predicts the onset of hemorrhagic shock. The sensor is based upon diffuse correlation spectroscopy (DCS). DCS measures fluctuations in near-infrared light scattering of blood cell motion in capillaries. DCS extracts th characteristic time constants due to mean blood flow velocity. The aims of the proposal are: 1. Integrate DCS system with physiological monitors, 2. Perform definitive measurements using the human lower body negative pressure (LBNP) model for hemorrhage. 3. Analyze DCS and physiological data and answer the following questions: Is normalization of subject-to-subject variation possible? Is subject-to-subject variability reduced by DRS-based determination of tissue scattering and absorbance properties? Is predictive value improved by addition of vital parameters and if so, what is the best approach to multiparametric smart algorithms? Is predictive value improved by measuring the change in ? with progressive bleed? 4. Perform LBNP studies under the US Army LBNP pressure to failure (presyncope) protocol. 5. Test the CBFM in a clinical setting during high-blood loss, human spinal surgery. 6. Complete all reports